1. Field of the Invention
The present invention relates to a resin-encapsulated semiconductor device in which a semiconductor element is bonded on inner leads of a lead frame and the surroundings thereof are encapsulated with a resin, and that allows other semiconductor devices or functional components such as a resistor to be stacked in a vertical direction.
2. Description of the Related Art
In recent years, in order to cope with miniaturized and high-density electronic equipment, high-density packaging of semiconductor components such as a resin-encapsulated semiconductor device has been demanded, and accordingly smaller and thinner semiconductor components have been developed. For example, the type of a package is being changed from a peripheral package in which external terminals are provided on the periphery of a semiconductor device to an area array package in which external terminals are provided in a grid pattern on a mounting surface of a semiconductor device. Further, semiconductor devices that are small and thin and yet have a large number of pins also have been developed.
Hereinafter, a conventional resin-encapsulated semiconductor device will be described. In recent years, a resin-encapsulated semiconductor device called “QFN (Quad Flat No-lead Package)” in which one side thereof is molded actually has been developed as a small and thin resin-encapsulated semiconductor device (see JP 2001-77277 A, for example).
Initially, the QFN-type resin-encapsulated semiconductor device in which a die pad is exposed on a bottom surface of a package will be described as a conventional resin-encapsulated semiconductor device. FIGS. 18A to 18D illustrate the conventional QFN-type resin-encapsulated semiconductor device; FIG. 18B is a plan view and FIG. 18A is a cross-sectional view taken along line I-I in FIG. 18B. In addition, FIGS. 18C and 18D illustrate a most commonly used QFP (Quad Flat Package)-type resin-encapsulated semiconductor device, in which external terminals protrude from a packaging resin toward a periphery thereof FIG. 18C is a cross-sectional view and FIG. 18D is a plan view.
As shown in FIGS. 18A and 18B, the conventional QFN-type resin-encapsulated semiconductor device has a structure in which a semiconductor element 52 is bonded on a die pad 51 of a lead frame and a plurality of inner lead portions 53 are arranged so that ends thereof are opposed to the die pad 51. Electrodes of the semiconductor element 52 are connected electrically with surfaces of the inner lead portions 53 via thin metal wires 54. The surroundings of the semiconductor element 52, the die pad 51, the inner lead portions 53, and the thin metal wires 54 are encapsulated with an encapsulating resin 55. Bottom surfaces and outer lateral surfaces of the inner lead portions 53 are exposed on a bottom surface and lateral surfaces, respectively, of the package from the encapsulating resin 55, so as to be arranged as external terminals 56.
Further, as shown in FIGS. 18C and 18D, the conventional QFP type resin-encapsulated semiconductor device also has a structure in which the semiconductor element 52 is bonded on a die pad 57 of a lead frame and a plurality of inner lead portions 58 are arranged so that ends thereof are opposed to the die pad 57. Electrodes of the semiconductor element 52 are connected electrically with surfaces of the inner lead portions 58 via thin metal wires 59. The surroundings of the semiconductor element 52, the die pad 57, the inner lead portions 58, and the thin metal wires 59 are encapsulated with an encapsulating resin 60. Trailing ends of the inner lead portions 58 protrude from lateral surfaces of the encapsulating resin 60, so as to be arranged as external terminals 61 on outer lateral surfaces of the package.
The lead frame used in the conventional resin-encapsulated semiconductor device, which is not shown in the figures, includes the die pad 51 arranged substantially at the center in an opening region of a frame, hanging lead portions 62 for supporting the die pad 51, one end of each of them being connected to each corner of the die pad 51, the other end thereof being connected to the frame, and the plurality of inner lead portions 53 arranged so that ends thereof are opposed to corresponding edges of the die pad 51.
In an attempt to make the conventional resin-encapsulated semiconductor device with these structures smaller and have higher density, the peripheral type semiconductor devices, such as QFN, in which external terminals are arranged on the periphery of the semiconductor devices, have been replaced by area array type semiconductor devices having higher density, such as BGA (Ball Grid Array), in which external terminals are arranged in a grid pattern on a bottom surface of the semiconductor devices. However, due to limitations on the processing of a line and space (design of a wiring pattern) of a substrate to be mounted and limitations imposed by a method of mounting by a reflow process using a solder cream, the smallest possible pitch of the external terminals that allows these semiconductor devices to be mounted on the substrate is 0.4 mm in the case of the peripheral type semiconductor devices such as QFN and 0.65 mm in the case of the area array type semiconductor devices such as BGA. Thus, further miniaturization and high-density packaging of the resin-encapsulated semiconductor devices are becoming difficult.
Further, there is a need for a semiconductor device commensurate with a higher functionality of sets typified by mobile phones and the like. In the case of a mobile phone, for example, a frequency band of not less than 1 GHz in use has been utilized already to realize stable communications or large-capacity data communications in a current industrial field of mobile communications (mobile phones, PDAs, and the like). In the future, there will be an increasing need for signal communications in a higher frequency band.